Conventional torque converter turbines are typically assembled from stamped pieces. The torque converter turbine shell, turbine core and turbine blades are stamped separately from one another. The blades have tabs on opposing edges. The tabs on a first edge are inserted into corresponding perforations in the shell. The core is then placed over the tabs on the second edges of the blades. The tabs passing through both the core and the shell are bent over, locking together the core, the shell and the blades into a single unit.
Turbines formed in this manner have three significant performance restricting limitations. Those limitations are: potential leak paths both between blade edges proximate to the core and the shell, and at the perforations in the shell and the case for the tabs; an inability to provide leading and trailing blade edges with desired radii and to vary the thickness of the blades significantly, effectively limiting the variety of air foil shapes; and high rotative inertia due to their being formed of steel.
Torque converter turbines molded of plastic address all of the aforementioned limitations of stamped turbines. The leak paths are eliminated with the blades, the core and the shell being molded simultaneously. There is much more freedom allowed in the design of airfoil shapes. The inertia of the turbine is significantly reduced.
Attempts have been made in the past to provide a plastic molded turbine in order to obtain the cited advantages. The interior of a torque converter, however is a harsh environment. The turbine is subjected to high levels of axial loading and torsion as well as being subjected to high operating temperatures. Turbines are typically splined to a torque converter output element or a transmission input element, and must transmit driving torque to the vehicle transmission. Plastic and plastic composites containing reinforcing fibers are generally unsuitable for this type of loading condition, so plastic molded turbines typically have been provided with a steel hub having splines for engaging the transmission input element. However, the harshness of the environment within the torque converter has made the joining of the steel hub with the rest of the turbine, a plastic bladed element, difficult. The different coefficients of thermal expansion of the steel and the plastic tend to stress the joint when it is subjected to a large change in temperature, making it difficult to sustain the high axial and torsional loads to which the turbine is subjected.